docs: def all_tokens(self, delimiter=' '):
          """
          Return a list of all tokens occurring in the label-list.
  
          Args:
              delimiter (str): The delimiter used to split labels into tokens
                               (see :meth:`audiomate.annotations.Label.tokenized`).
  
          Returns:
               :class:`set`: A set of distinct tokens.
          """
          tokens = set()
  
          for label in self:
              tokens = tokens.union(set(label.tokenized(delimiter=delimiter)))
  
          return tokens